Human chromosomes are classified by size and location of centromeres on chromosomes:
Group A: Chromosomes 1-3; metacentric
Group B: Chromosomes 4 and 5; submetacentric
Group C: Chromosomes 6-12; submetacentric
Group D: Chromosomes 13-15; acrocentric with satellites
Group E: Chromosomes 16-18; short metacentric or submetacentric
Group F: Chromosomes 19 and 20; short metacentric
Group G: Chromsomes 21 and 22; short acrocentric chromosomes, 21 is shorter than 22
X chromosomes can be placed with Group C; Y chromosomes which have no satellites can be placed with Group G.
2. Review the basic concept of chromosome banding. (p.125-126, 132)
Preparation
(1) Draw blood
(2) Remove RBCs (which don't have any DNA); ficoll separation of lymphocytes for culture
(3) Culture in phytohemagglutin for 2-3 days - phytohemagglutin is a mitogen that encourages faster cell division
(4) add colchicine - inhibits microtubule formation to prevent chromosome separation
(5) treat in hypotonic solution
(6) drop cell suspension on slide (explodes because of hypotonic treatment)
(7) air dry
(8) stain using specific technique:
Q-bands: quinacrine staining - bright flourescent bands
G-bands: giemsa staining after chromosome pretreatment - dark G-bands correspond with most bright Q-bands
R-bands: various techniques - inverse pattern compared to G and Q; useful for defining ends of chromosomes
T-bands: various technuqies - highlights end of chromosomes
C-bands: Protein/DNA extraction with Giemsa staining - highlight centromeric regions
NOR: silver staining - stains nucleolus organizer regions (acrocenteric chromosomes in humans)
Characteristic
R-bands
Q/G-bands
C-bands
Location
Chromosome arms
Chromosome arms
Centromeres, distal Y
Base composition of DNA
GC-rich
AT-rich
AT-rich and some GC-rich
Type of chromatin
Euchromatin
Heterochromatin
Heterochromatin
Time of DNA replication
Early S
Mid to late S
Late S
Transcriptional activity
High; housekeeping
Low; tissue-specific
Absent
3. Interpret in a diagram of a chromosome: arm region, band, and centromere. (p.123)
(1) chromatid
(2) centromere
(3) p arm (p for petite)
(4) q arm
4. Explain the correct karyotype reporting procedure. (p.127)
To report a given karyotype, record the total chromosome number, sex chromosomes. If there is an extra chromosome, record the total chromosome number, sex chromosomes, +extra chromosome
Examples
Normal: 46, XY
Trisomy 21: 47, XY, +21
For chromosome banding notation, record
(1) chromosome number
(2) arm
(3) region number
(4) band number
(5) sub-band number as a decimal
Example
1Q25.1: chromosome 1, Q arm, region 2, band 5, sub-band 1
5. Illustrate the numerical chromosome abnormalities: give one example. (p.139)
Numerical chromosome abnomalities are abnormalities involving an incorrect number of chromosomes. Ploidy can result from failure of the egg to expel its second polar body upon completion of the second meiotic division at fertilization or polyspermy when two sperm penetrate the egg when the cortical granule reaction fails to respond in time. Trisomy can result from non-disjunction of chromosomes either during meiosis I or meiosis II.
Karyotype
Comment
92, XXYY
Tetraploidy
69, XXY
Triploidy
47, XX, +21
Trisomy 21
47, XX, +18
Trisomy 18
47, XX, +13
Trisomy 13
47, XX, +16
Trisomy 16
47, XXY
Klinefelters syndrome
47, XXX
Trisomy X
45, X
Turner syndrome
49, XXXXY
Variant of Klienfelters syndrome
6. Explain major chromosome aneuploidy syndromes compatible with live birth. (p.147)
Trisomy 21 is a major chromosome aneuploidy syndrome can be compatible with live birth. Trisomy can result from non-disjunction of chromosomes either during meiosis I or meiosis II.
Characteristics: mental retardsation, flat nose, close-set eyes, slanding eyelids, protruding tongue, 1 in 800-1000 births, due to maternal age with 85% maternally derived abberration likelihood.
7. Explain structural chromosome abnormalities and how those happen. (p.147-148)
Chromosome structural abnormalities are errors within a chromosome that can result from chromosomal breakage. Breakage of chromosomes creates two unstable, sticky ends that can be incorrectly rejoined by repair mechanisms. Breakages can be caused by exposure to ionizing radiation, rare inherited conditions, x-rays, and chemical mutagens.
Structural aberrations that can occur include:
Deletion
Ring chromosomes
Duplications
Inversions
Centric fragments
Acentric fragments lack a centromere and are lost because they cannot bind the the spindle apparatus during mitosis
Objectives
1. Classify the human chromosomes. (p.129)
Human chromosomes are classified by size and location of centromeres on chromosomes:
Group A: Chromosomes 1-3; metacentric
Group B: Chromosomes 4 and 5; submetacentric
Group C: Chromosomes 6-12; submetacentric
Group D: Chromosomes 13-15; acrocentric with satellites
Group E: Chromosomes 16-18; short metacentric or submetacentric
Group F: Chromosomes 19 and 20; short metacentric
Group G: Chromsomes 21 and 22; short acrocentric chromosomes, 21 is shorter than 22
X chromosomes can be placed with Group C; Y chromosomes which have no satellites can be placed with Group G.
2. Review the basic concept of chromosome banding. (p.125-126, 132)
Preparation
(1) Draw blood
(2) Remove RBCs (which don't have any DNA); ficoll separation of lymphocytes for culture
(3) Culture in phytohemagglutin for 2-3 days - phytohemagglutin is a mitogen that encourages faster cell division
(4) add colchicine - inhibits microtubule formation to prevent chromosome separation
(5) treat in hypotonic solution
(6) drop cell suspension on slide (explodes because of hypotonic treatment)
(7) air dry
(8) stain using specific technique:
Q-bands: quinacrine staining - bright flourescent bands
G-bands: giemsa staining after chromosome pretreatment - dark G-bands correspond with most bright Q-bands
R-bands: various techniques - inverse pattern compared to G and Q; useful for defining ends of chromosomes
T-bands: various technuqies - highlights end of chromosomes
C-bands: Protein/DNA extraction with Giemsa staining - highlight centromeric regions
NOR: silver staining - stains nucleolus organizer regions (acrocenteric chromosomes in humans)
3. Interpret in a diagram of a chromosome: arm region, band, and centromere. (p.123)
(1) chromatid
(2) centromere
(3) p arm (p for petite)
(4) q arm
4. Explain the correct karyotype reporting procedure. (p.127)
To report a given karyotype, record the total chromosome number, sex chromosomes. If there is an extra chromosome, record the total chromosome number, sex chromosomes, +extra chromosome
Examples
Normal: 46, XY
Trisomy 21: 47, XY, +21
For chromosome banding notation, record
(1) chromosome number
(2) arm
(3) region number
(4) band number
(5) sub-band number as a decimal
Example
1Q25.1: chromosome 1, Q arm, region 2, band 5, sub-band 1
5. Illustrate the numerical chromosome abnormalities: give one example. (p.139)
Numerical chromosome abnomalities are abnormalities involving an incorrect number of chromosomes. Ploidy can result from failure of the egg to expel its second polar body upon completion of the second meiotic division at fertilization or polyspermy when two sperm penetrate the egg when the cortical granule reaction fails to respond in time. Trisomy can result from non-disjunction of chromosomes either during meiosis I or meiosis II.
6. Explain major chromosome aneuploidy syndromes compatible with live birth. (p.147)
Trisomy 21 is a major chromosome aneuploidy syndrome can be compatible with live birth. Trisomy can result from non-disjunction of chromosomes either during meiosis I or meiosis II.
Characteristics: mental retardsation, flat nose, close-set eyes, slanding eyelids, protruding tongue, 1 in 800-1000 births, due to maternal age with 85% maternally derived abberration likelihood.
7. Explain structural chromosome abnormalities and how those happen. (p.147-148)
Chromosome structural abnormalities are errors within a chromosome that can result from chromosomal breakage. Breakage of chromosomes creates two unstable, sticky ends that can be incorrectly rejoined by repair mechanisms. Breakages can be caused by exposure to ionizing radiation, rare inherited conditions, x-rays, and chemical mutagens.
Structural aberrations that can occur include: